Polymeric insecticidal compositions in the form of pellets, granules or film have been widely used as a means of providing a slow release, long term insecticide formulation which kills insects contacting or coming within close proximity of the pellets, granules or film. Such formulations are widely used in agricultural and domestic applications by spreading or distributing the pellets, granules or film containing the insecticide in the area to be protected. Generally, these formulations are designed so that insecticide therein gradually diffuses to the surface of the polymer so that it will be transmitted to an insect coming into contact or close proximity therewith. Thus, over a period of time, the insecticide is released from the formulation until the pellets, granules or film is no longer effective in killing insects and must be replaced. Typically, the reported useful retention time of the insecticide ranges from a month to two or three years at the most.
In many instances, it is desirable to form useful articles from a thermoplastic composition. In certain applications, however, these useful articles are subject to insect attack and it is, therefore, desired that such articles have resistance to attack from insects. For example, in electrical wiring installations, nonresistant junction boxes and cable jackets are frequently invaded by ants or crickets, creating fire and safety hazards to personnel, often interrupting electrical service, and necessitating replacement of the junction box or cable. Also, nonresistant tubing in drip irrigation systems which has been damaged by ants, for example, results in improper distribution of water, wasting water and often damaging crops, as well as necessitating replacement of the tubing.
In manufacturing useful articles which are insect resistant, the insecticidal thermoplastic compositions heretofore known have been of limited utility. Because of the diffusion of the insecticide from the thermoplastic composition, it has heretofore been necessary to incorporate as high a percentage of the insecticide in the polymer as is possible without phase separation or insecticide exudation in order to extend the insecticide retention time thereof. In most systems, however, the maximum insecticide concentration has been quite low, for example, 1.8-2 weight percent in the polyethylenehalopyridyl phosphate system. Moreover, the high content of the insecticide has adversely affected the desirable physical properties of the composition. These adversely affected properties include those desirable for end use as useful articles, such as resistance to creep and stress crack, tensile strength, yield strength and elongation, and those necessary for processability. On the other hand, if the insecticide content is reduced to the extent that the physical properties of the polymer are not adversely affected, the retention time of the insecticide is correspondingly decreased so that useful articles formed from the thermoplastic composition lose their resistance to insect attack long before the useful lifetime of the article has expired. Thus, when formed from the heretofore known thermoplastic insecticidal compositions, articles such as electrical junction boxes, jackets for electrical cables, and tubing for drip irrigation which are subjected to insect attack after losing resistance thereto must be replaced substantially prior to expiration of the useful life thereof which would normally be expected in the absence of such insect attack.